1. Field of the Invention
The invention relates generally to the field of well head equipment used in oil and gas well services. More specifically, the present invention relates to an apparatus that provides a pressure seal around a slick cable used in oil field operations.
2. Description of the Prior Art
The use of so called “wireline” conveyance equipment and procedures are well known in the oil and gas industry for running a multitude of different types of well tools and other well equipment in oil and gas wells while the wells are under pressure. For example, in well logging operations, two basic types of wireline conveyance have traditionally been used, slickline and twisted or braided cable. The twisted or braided cable typically consists of a large-diameter cable that mechanically supports a hanging instrument. A wireline truck on the surface will usually be required for support. A data cable of this type supplies power and provides a communication connection down the well to the instrument in the well bore. Slickline, on the other hand, is typically a smaller diameter line in the form of a solid wire on the order of ⅛ inch or smaller, e.g., like piano-wire and does not typically provide real time data at the well surface.
Slickline logging tools have been developed in recent years to enable data collection in deep oil and gas wells. The well casing is completed by setting pipe and grouting it in place with cement. The cement seals the annulus between the soil and the outside diameter of the pipe. The top of the pipe is threaded and a blow-out preventer is installed. Some type sealing device will typically be provided on the upper end of the upper tubing section which will permit the wireline to move into and out of a lubricator while the lubricator is under pressure form the well. A closing valve, such as a gate valve, and a second pipe provide a sealed enclosure above the well head. The sealed enclosure is long enough to accommodate a logging tool with a top sub attached to the slickline cable. The cable exits the lubricator through a sealing gland that enables the slick line to enter the sealed enclosure under pressure. When the gate valve is fully opened, the logging tool descends into the well casing, while the sealing device maintains a seal with the slick line as the hoist lowers the logging tool into the well bore.
Conventional slickline logging tools are designed with internal recording memory to log data during descent and ascent in the hole. After returning from the well, recorded digital data is read out on the surface and chart recordings are used to display the data for analysis. Twisted or braided cable, on the other hand, may provide real time data communication to the well surface. The wireline or cable not only serves to support the tools and other equipment when running them into and withdrawing them from a well, but may also be used to apply forces when manipulating tools and other equipment present in the well.
Depending upon the particular type of equipment present, the sealing device referred to above may take the form of a what is referred to as a stripper, stuffing box, sealing gland, pack-off heads, etc. In each case, the device performs the safety function of pressure containment during wireline operations. For example, wireline (or slick-line) pack off heads (oil savers) have been used by the oil field service industry for many years. A pack off head is designed to make a pressure seal around a wireline to contain the well pressure during trips in and out of the well. If during wireline operations a well kick were experienced, an unsafe condition would occur if the well head was not contained but instead left open to atmosphere. A typical pack off head includes a hard rubber insert with a passage where the wire line passes through the annulus. To seal around the wireline, the hard rubber insert is axially compressed, which reduces the cross sectional area of the passage. Reducing the cross sectional area of the passage causes the inner radius of the passage to fit snugly around the outer radius of the wire line, thus preventing fluid flow through the passage. The typical prior art pack off head only functioned to seal around a static line. This was due at least in part to the fact that the prior art braided cable would quickly destroy the seal if it moved though the energized seal element in use.
Traditionally, pack off heads have been manual or hydraulic. A manual style pack off head is usually comprised of a threaded cap that compresses the rubber packing element as the cap is screwed down onto the head assembly. This operation is typically performed by hand. The hydraulic style pack off head has a hydraulic cylinder that is expanded via hydraulic pressure provided by a hand pump connected to the head by a hydraulic hose. The pack off head hydraulic cylinder moves as pressure is supplied to it, expansion of the pack off head hydraulic cylinder in turn compresses the pack off element to provide a seal around the wireline.
Despite the advances which have been made in the wireline arts, there continues to exist a need for improvements in the area of cable conveyance pressure containment devices of the type discussed above. For example, while slick line or braided cable have been widely used in the past, new types of “slick cable” are now beginning to appear on the scene. The slick cable will have a smooth outer diameter in the same manner as traditional slick line, while allowing real time data communication with the downhole tool in the well bore in the manner of traditional braided cable. Preferably, the new slick cable will be capable of dynamic movement through the seal elements, even when the seal elements are energized to contain well pressure. The outer diameter of these types of slick cable will be much larger than traditional slick line, e.g., larger than ½ inch. New pressure containment devices are needed which have the ability to accept these new types of slick cable.